Here are the RMAA results for the iPod Classic (2009), the Samsung Galaxy Nexus, and the FiiO E7. The iPod was tested via it's Line Out Dock, as well as its headphone out, unloaded, and loaded with Sony MDR-XB700 headphones (24 ohms). The Galaxy Nexus and E7 were tested via their headphone out, loaded and unloaded. Here's a comparison between the 3, loaded with the headphones.

Audiophiles always say that the iPod's LOD outputs a "cleaner" signal than its headphone out; if I'm reading the values and graphs right, that seems correct. I couldn't say whether the difference is audible; one would have to also test the external headphone amplifier that would be connected to the LOD.

Overall the E7 seems superior, while the iPod is a pretty close second in some aspects, especially if you consider the LOD results. Of note is the significantly worse stereo crosstalk result from the Galaxy Nexus.

Edit: I used an old laptop for the recordings. I'm considering investing in a decent USB device. If I do get one, I'll run RMAA again.

You said in the other thread that you've got the volume cap on your ipod. If so, you need to either remove that so that you can use the full dynamic range of the ipod, or else set the level on the other players to be identical to the ipod. Otherwise you're basically handicapping the ipod by not letting the DAC use its full SNR.

Sure it can. I know for a fact that we don't implement it in rockbox, since i reviewed some of the patches for the ipod 6G's sound driver

QUOTE (skamp @ Apr 26 2012, 16:37)

How does the volume of the recording affect the results? I didn't match the volumes. Are my results useless?

The frequency response will be unaffected, but it will probably make everything else look worse by about however many dB its capped. Both because they will be worse, and because your sound card will probably struggle to record such weak signals without introducing more noise.

.. those are a lot better. I tend to think that the system you recorded with actually has a higher noise floor then the devices you were testing so maybe the SNR results aren't going to be right regardless. Still, good to know all of the devices you tested have very high SNR

Well, I dusted off my old PC and tried three different PCI sound cards that were lying in a box. I got much better results with the Terratec Aureon Sky 5.1 (which wasn't the most expensive of the bunch). I measured a DR of about 92 dB. The iPod LOD is actually the winner with that setup, but all devices fared quite well (see individual results).

Well, I dusted off my old PC and tried three different PCI sound cards that were lying in a box. I got much better results with the Terratec Aureon Sky 5.1 (which wasn't the most expensive of the bunch). I measured a DR of about 92 dB. The iPod LOD is actually the winner with that setup, but all devices fared quite well (see individual results).

Which kinda proves a point I've been trying to make with some success for years, and that building a good potentially sonically transparent audio interface isn't exactly rocket science and doesn't take a NASA-sized budget.

On another forum, I recently saw a poster who just invested in this combo:

"I have just begun to convert some LPs to 192/24 digital files using PureVinyl and a TC Impact Twin." The interface runs close to $400 and the software runs about $130. I can see exactly what they offer as compared to simpler approaches, such as the ART USB Phono Plus Interface and Audacity, but the perceived need for all of these sound-modifying tools sort of shoots holes in the idea that the LP sounds superior all by itself. ;-)

Looks like you should inspect that one for any misimprovements present in the processing chain. Its sound implementation does not seem to be that great, but there is definitely something else going on that dominates the results. I'd say there's EQ and dynamic compression in use, presumably for better speaker audio. ICEpower would be referring to Class-D speaker amps.

BTW, measuring DAPs at anything else than 44.1 kHz is a potentially risky business. At least keep in mind that sample rate does matter.

I still have two of the aforementioned Terratec cards in use. As you found out, they are quite flexible when it comes to recording levels. They apparently were a co-development with ESI/Audiotrak at the time. I'd need to reverse engineer the headphone amp at some point, which I am told uses a Class B buffer (I never liked the result with anything less than 300 ohms much, though according to measurements coupling caps may be the bigger issue).

Those measurements look a bit strange for the ipod (in headphones), I mean the lobes around the 1kHz sine wave. Were you using it plugged into a power adapter? A smps supply could cause that. They dissapear on the rockbox version which I think is interesting. It would be good to find out why.

All tests were run on battery. Note that the lobes disappear with the LOD and stock firmware too. The big difference is the maximum volume. The stock firmware suffers from a substancial volume cap (6-10 dB I think) on the headphone out, which neither the LOD with stock FW nor Rockbox have.

Those measurements look a bit strange for the ipod (in headphones), I mean the lobes around the 1kHz sine wave. Were you using it plugged into a power adapter? A smps supply could cause that. They dissapear on the rockbox version which I think is interesting. It would be good to find out why.

Those kinds of "lobes" are usually windowing artifacts. IOW, the data and the time window that was applied to it were mismatched.

I got an EMU 0204 USB and made new measurements. I think I need a better stereo splitter cable for loaded tests, because the stereo crosstalk values are suspiciously high. I even managed to squeeze out 7 more decibels in one case just by wiggling the jack :-/

I got an EMU 0204 USB and made new measurements. I think I need a better stereo splitter cable for loaded tests, because the stereo crosstalk values are suspiciously high. I even managed to squeeze out 7 more decibels in one case just by wiggling the jack :-/

On second thought, I'm not sure my stereo splitter cable is to blame. When connected only to the EMU's line-in, without headphones attached, I get crosstalk values below -90 dB. I've also found othermeasurements of the Clip+ on the web that match mine, so I guess that high stereo crosstalk value is pretty much accurate. It's ABXable on material with content in one channel and silence in the other.

Interesting measurements. I'm very surprised how EMU 0204 performs well comparing to O2 DAC without load, but not so great with your low impedance D2000 (25 Ω). EMU performs weird and that isn't surpise as it wasn't designed for low impedance phones. Its output impedance is 22 Ω. However it should performs well with high impedance phones.

I have similar EMU Pre Tracker USB and use it with HD650 and HD800 ( variable impedance, >325 Ω; ) . Considering the main rule of thumb (nwavguy's) Zphones/8 EMU USB interfaces (22 Ω, Zo) should drive 250 Ω and higher impedance phones without any issue.

Shortly, it will be interesting to see your measurements with O2 and EMU 0204 with 300 Ω phones.I'm not sure it will be enough correct to use variable resistor (potentiometer) as dummy load because an impedance of high-z phones is actually variable per frequency (see the previos graph). One way around is to use quite simple filters RLC for more realistic simulation of phones as a load, that shouldn't be difficult. Or just get a real 250-300 Ω phones.

BTW, as I have already mention to You on irc channel about my impressions of E17. Mmm, I prefer EMU Pre Tracker after all. Simply, it's cleaner. So I suspect that EMU interfaces could be comparable with state of art O2 DAC/AMP when used with high-z phones.